Japanese Patent Application Publication No. 2002-372117 (Patent Document 1), Japanese Patent Application Publication No. 2002-372118 (Patent Document 2), Japanese Patent Application Publication No. 2011-141027 (Patent Document 3), and Japanese Patent Application Publication No. 2011-142802 (Patent Document 4) each disclose a structure of a linear actuator comprising a motor portion 201; an output screw shaft 205; a screw nut 207; a thrust radial bearing 209; a lock nut 210; and a bolt not shown. The motor portion 201 includes a hollow rotary shaft 203. The output screw shaft 205 is operable to coaxially pass through the hollow rotary shaft 203. The screw nut 207 is located inside the hollow rotary shaft 203 and is screwed onto the output screw shaft 205. The screw nut 207 includes a flange portion 207A projecting radially outwardly from one axial end 203A of the hollow rotary shaft 203. The thrust radial bearing 209 is operable to rotatably support the hollow rotary shaft 203 on the side of the one axial end 203A of the hollow rotary shaft 203. The lock nut 210 is screwed onto the outer peripheral surface of the hollow rotary shaft 203 on the side of the one axial end 203A to fix the thrust radial bearing 209. The bolt not shown is operable to fix the flange portion 207A of the screw nut 207 to the lock nut 210 (refer to FIG. 3).